The invention relates to a method for reducing the pollutant emission of an internal combustion engine according to the introductory part of claim 1.
Various devices and methods for exhaust purification are already known.
EP-B-0 561 311 for example relates to an exhaust purification device comprising a zeolite-based adsorber for the short-time intermediate storage of pollutants, and a catalytic converter disposed downstream thereof for the conversion of the pollutant. In the exhaust tube section lying therebetween there opens a tube which is sufficiently distanced from the adsorber and which comes from a burner with its own fuel and air supply. By way of this arrangement it is made possible that on the one hand the gases produced by the burner heat the catalytic converter and bring it quickly to its operating temperature without compromising the zeolite adsorber, and that on the other hand thermic secondary reactions of exhaust components are achieved in the mentioned exhaust tube section, i.e. still before the entry into the converter.
According to DE-OS 41 41 946 it is suggested in a similar context to blow secondary air into the exhaust stream between the internal combustion engine and the catalytic converter. To this effect however an air pump is provided whose starting up is effected in a directed manner only for so long until the operating temperature of the catalytic converter is reached.
In addition with DE-OS 37 23 703 air is mixed in with the exhaust stream before entry into the catalytic converter. In contrast to the two above-mentioned solutions a separate gas or air delivery means is done away with in that the internal combustion engine itself forms the delivery means. To this effect it is provided for some of the cylinders not to be fired but to be applied as air pumps.
DE-PS 40 29 672 suggests the improvement of cutting off individual cylinders only for a short time, i.e. to let a short interruption follow several working strokes so that the temperature of the cylinders remains maintained. Generally it is also advantageous to cut off the ignition according to the interruption of the supply of the mixture.
The documents cited hereinabove relate to improvements in the starting procedure of an internal combustion engine, i.e. in particular of an Otto engine of a road vehicle. Indeed the pollutant emission during the starting of a vehicle is increasingly important, since on the one hand exhaust regulations are becoming more restrictive and on the other hand the pollutant emission during the normal operation is reduced thanks to more effective catalytic converters.